AutoCodes – Mercury – P1128 Mercury

P1128 Mercury Code - Front O2 Sensor Connectors Swapped

Quick Answer

The Diagnostic Trouble Code (DTC) will set anytime the Powertrain Control Module (PCM) Detects Upstream Oxygen Sensors swapped from Bank to Bank. Common causes include Crossed HO2S Harness Connectors, Powertrain Control Module (PCM) Harness Connector. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P1128 Mercury indicates Front O2 Sensor Connectors Swapped.
Common causes: Common causes include Crossed HO2S Harness Connectors, Powertrain Control Module (PCM) Harness Connector.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 1,797

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Aug 03, 2020

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Cost to Diagnose
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Code P1128 Mercury Description

The Diagnostic Trouble Code (DTC) will set anytime the Powertrain Control Module (PCM) Detects Upstream Oxygen Sensors swapped from Bank to Bank. Heated Exhaust Gas Oxygen (HEGO) Sensor Monitor checks & determines if the HO2S signal response for fuel shift corresponds to the correct engine bank. The code sets when HO2S being tested is not indicated.

OBDII Code P1128 Mercury - Front O2 Sensor Connectors Swapped - AutoCodes.com — P1128 Mercury Code - Front O2 Sensor Connectors Swapped

What does this mean?

What are the Possible Causes of the DTC P1128 Mercury?

Crossed HO2S Harness Connectors
Powertrain Control Module (PCM) Harness Connector

How to Fix the DTC P1128 Mercury?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P1128 Mercury code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.